1. Field of the Invention
This invention relates to a structure of a connector used for a microphone, and more particularly to a structure of a connector connecting a dedicated cord and a microphone unit or a power module in a capacitor microphone.
2. Description of the Related Art
Usually, a capacitor microphone has a high impedance in a microphone unit, and includes an impedance converter constituted by a field effect transistor (FET).
With a tiepin or gooseneck type microphone, a microphone unit itself houses an impedance converter therein in order to make the microphone less visible. Further, a low-cut circuit and an output circuit are housed in separate circuit housings, and a dedicated microphone cable is used to connect the microphone unit and the circuit housing. The microphone unit converts voices into electric audio signals, which are transmitted to the circuit housing, and are output from the output circuit. Such a circuit housing is called a “power module”.
The dedicated microphone cable connecting the microphone unit and the power module is a 2-conductor shielded cable, and is constituted by a power wire supplying power to the microphone, a signal wire inputting the audio signals to the power module, and a shielded cable which electrostatically shield the power wire and signal wire.
The audio signal is transmitted in an unbalanced state through the microphone cable, and suffers from poor immunity to external noise, i.e., is adversely affected by external electromagnetic waves. Specifically, external electromagnetic waves arriving at the microphone cable enter into the microphone unit or power module, are detected by a semiconductor device composing the microphone unit or power module, and are mixed into the audio signals as noise.
A microphone output is output from the power module via a balanced shielded cable. When strong electromagnetic waves are applied to the microphone or the output cable of the microphone, a high frequency current runs through a microphone connector and gets into the microphone, where the high frequency current is demodulated by a semiconductor device, and is output as audio frequency noise via the microphone.
A cable connector 10 shown in FIG. 6(A) of the accompanying drawings is connected to one end of a dedicated microphone cable. The cable connector 10 is fitted into a receptacle 30 shown in FIG. 5(A). Specifically, the cable connector 10 includes three thin cylinders 11 embedded therein, which receive three pins of the receptacle 30. Terminal blocks 12 integral with the thin cylinders 11 extend outward from a rear surface of the cable connector 10 (the right end in FIG. 6(A)). Two conductors and a shielded wire of the microphone cable, not shown, are soldered to their corresponding terminal blocks 12. An insulating sleeve 60 is attached around the microphone cable, surrounds a joint of the terminal blocks 12 and the microphone cable, and protects the joint against short-circuiting. The insulating sleeve 60 is as thick as the connector 10.
A cylindrical part 71 of a crimp 70 is fitted into a rear end of the insulating sleeve 60. The crimp 70 has a plurality of claws 72 at its rear half. The claws 72 are pressed onto an insulating sheath of the microphone cable, so that the crimp 70 is integral with the microphone cable.
The cable connector 10 is fitted into a cylindrical connector housing 50. The connector housing 50 is long enough to hold the cable connector 10, the insulating sleeve 60 and the cylindrical part 71 of the crimp 70. A rear end of the connector housing 50 is fitted into a front end of the bush 40, which is slightly thicker than the microphone cable, and has a tapered end 141 and a cover 142 which is thicker than the tapered end 141. The microphone cable is put through a center opening of the tapered end 141.
The cable connector 10 and the receptacle 30 (shown in FIG. 5) are of so-called 3-pin type. No. 1 pin is used for the shielded wire of the microphone cable, is electrically connected to the connector housing 50, crimp 70 and bush 40, and is grounded. A signal conductor and a power conductor of the microphone cable are respectively connected to No. 2 and No. 3 pins.
FIG. 5(A), FIG. 5(B) and FIG. 5(C) show the structure of the receptacle 30. The receptacle 30 is a metal cylinder, and has a male screw 31 on a peripheral surface thereof, and a flange 33 at one end thereof (shown at the right side in FIG. 5(A)). The receptacle 30 is put into the power module or the like through an opening thereof. A nut is engaged into the male screw 31 via an inner wall of a power module housing. Hence, the receptacle 30 is fixed to the power module housing with the nut and flange 33 holding opposite surfaces of the power module housing. The receptacle 30 has a bottom which is opposite to the flange 33. A relatively large and thick bottom plate 32 made of an insulating material is fixed to, screwed to or fitted to the bottom of the receptacle 30. Three pins 41 pass through the bottom plate 32. One end of a plug shown in FIG. 6 is inserted into the receptacle 30. Specifically, referring to FIG. 6, a left part of the connector housing 50 is inserted into the receptacle 30. The three pins 41 are fitted into the three thin cylinders 11 of the cable connector 10, respectively. The three pins 41 are used for grounding, transmitting and receiving signals, and supplying power. The three pins 41 partially extend outward from the bottom plate 32, and function as connector terminals 42, which are connected to the power module and so on using wires.
As described above, the receptacle 30 attached to the power module or microphone unit has to be grounded by connecting No. 1 grounding pin to the power module or microphone unit housing. Usually, the connecting terminal 42 of No. 1 pin is connected using an electric wire to a grounding point of the power module or the microphone unit. However, this arrangement tends to introduce high frequency currents into the power module or microphone unit. High frequency currents are demodulated by an impedance converter, and are outputted as audible frequency noise via the microphone.
For the purpose of short-circuiting high frequency currents between No. 1 and No. 2 pins and between No. 1 and No. 3 pins, ceramics capacitors (i.e., chip devices) are soldered across No. 1 and No. 2 pins and across No. 1 and No. 3 pins. However, in such a case, the pins tend to be minutely displaced each time the plug is attached into or detached from the receptacle 30. There is a problem that the ceramics capacitors are subject to stresses via soldered parts thereof, and will be broken.
In order to overcome the foregoing problem, it is conceivable to mount ceramics capacitors on a printed circuit board, to connect them between No. 1 and No. 2 pins and between No. 1 and No. 3 pins using printed wirings. The printed wiring pattern used for the grounding should be reliably connected to the receptacle 30 in order to cope with high frequency signals. However, with the foregoing arrangement of the related art, a number of improvements have to be made in order to block high frequency signals.
At present, as cellular phones become very popular, high frequency electromagnetic waves are present anywhere, and more high frequency signals tend to enter into audio signals. Especially, a capacitor microphone is easily susceptible to noise caused by high frequency signals from cellular phones arriving via the connector.
Up to now, proposals have been made in order to cover microphone bodies using cylindrical sheaths as disclosed in Japanese Patent Laid-Open Publications No. 2002-152,892 and Hei 11-155,198. No special emphasis has been placed on shielding of connectors as described above. Therefore, high frequency electromagnetic waves tend to enter into the connector, which causes noise to be mixed into audio signals.
The assignor of this application has proposed a structure which couples a microphone housing to a grounding terminal of a connector with a minimum impedance in the patent application (Japanese Patent Laid-Open Publication No. Hei 11-341,583, for example). Especially, the structure has been designed to effectively ground the connector. However, it does not have a concept of installing capacitors between pins in order to block external high frequency signals.
In order to overcome problems of the related art, the present invention is aimed at providing a microphone connector, in which capacitors made of chip devices are disposed between pins in order to block external high frequency signals, and are not broken even if the pins are displaced when attaching and detaching a plug to and from a receptacle.
Further, the invention provides a microphone connector which reliably blocks external high frequency signals.